It depends of the series really. Some of the more popular series like Naruto and Bleach have the raws on all those mega fansites while other are hosted on smaller sites. Tell us the series that you're looking for so we can help give you the sites.

There's always #lurk and Tokyo Toshokan. Sometimes they have raw volumes of manga. (Tokyotosho usually has the raw chapters available before scanlations.)

When it comes to raws on IRC, #udanraws is better solution than #lurk.
Udanraws is a branch of lurk that don't have as many visitors as lurk
so you won't get confused when you come around and is dedicated to
raws only.
My little raw fserve is there also, and I have some series that you won't
find unless you know how to use 'Share'.

Emule is also a good solution, but sometimes you won't get to know
if your raws are Japanese, Chinese or Korean so it may be confusing..